A conventional stator of a rotating electric machine will be described with reference to FIGS. 14 to 18.
FIG. 14 is a longitudinal cross-sectional view of an upper half portion of a stator core and a rotor of a rotating electric machine. FIG. 15 is a transverse cross-sectional view of FIG. 14, schematically showing a flow of cooling gas at a ventilation duct portion.
As shown in FIGS. 14 and 15, the stator of the rotating electric machine includes a cylindrical stator core 1, which is made up of a plurality of electromagnetic steel plates 2 that are stacked, and stator coils 7, which are contained in slots 6 that are formed at an inner circumference side of the stator core 1. The stator coils 7 latch into the slots 6, held by wedges 8 from the inner circumference side of the stator core 1. The wedges 8 have a shoulder portion that is wider than the width w of the slots 6. The wedges 8 are inserted along grooves that are provided on core tooth portions 9 along an axial direction.
Every time a predetermined number of electromagnetic steel plates 2 are stacked, a ventilation duct 5 is formed to allow cooling gas of the radial direction of the stator core 1 to pass therethrough. A peripheral portion of each of the ventilation ducts 5 is made up of at least one or more first inner spacers 4T, which are inserted between the electromagnetic steel plates 2 of the core tooth portions 9 that form the slots 6 of the stator core 1; at least one or more second inner spacers 4S, which are inserted at stator core outer side positions of the stator coils 7; and the electromagnetic steel plates 2, which are so disposed as to be spaced apart by the inner spacers 4T and 4S. The second inner spacers 4S, which are inserted at the stator core outer side positions of the stator coils 7, extend to stator core outer circumference portions of the slots 6. The first inner spacers 4T extend to inner circumference portions of the core tooth portions 9 of the stator core 1. Therefore, the stacked electromagnetic steel plates 2 are kept bonded together. The stator core 1 is clamped with end flanges, which are not shown in the diagrams, at the both ends of the stator core 1 in the direction of a rotational axis.
When the rotating electric machine having the stator described above is operated, the stator coils 7, among other things, generate heat due to electric current. The stator core 1 also generates heat as eddy current and the like emerge. In order to cool down the above, cooling gas 11 flows into the ventilation ducts 5 to cool the stator coils 7 and the stator core 1.
FIG. 16 is a schematic diagram showing paths the cooling gas takes in the ventilation ducts. As shown in FIG. 16, the stator core 1 includes core blocks 3, which are disposed at predetermined intervals in the axial direction, and the ventilation ducts 5.
The ventilation ducts 5 are divided into two sections: inlet sections 12, in which the cooling gas 11 flows from the outer side of the stator to the inner side; and exhaust sections 13, in which the cooling gas 11 flows from the inner circumference side of the stator to the outer circumference side. The sections 12 and 13 are alternately arranged in the direction of the axis of the core. The cooling gas 11 comes out of fans, which are not shown in the diagram, that are attached to both ends of a rotor 15. The cooling gas 11 is supplied into a gas gap 14, which is a gap between the stator core 1 and the rotor 15, from the outer circumference side of the stator core 1, an inner part of the rotor 15 and an end portion of the stator core. The cooling gas 11 that flows to the outer circumference side of the stator core passes through the ventilation ducts 5 of the inlet sections 12 to cool the core 1 and the stator coils 7 before being discharged into the gas gap 14.
The cooling gas 11 discharged from the inlet sections 12 and the cooling gas 11 that flows into the gas gap 14 directly from the end portion of the stator core are supplied to the ventilation ducts 5 of the exhaust sections 13 after flowing through the gas gap 14 in the axial direction. At this time, the cooling gas 11 discharged from the surface of the rotor after passing through the rotor 15 also flows together in the gas gap 14; and passes through the exhaust sections 13 to cool the stator coils 7 and the stator core 1 before being discharged to the outer circumference side of the stator. After flowing out from the outer circumference side of the stator, the cooling gas 11 is cooled down by a gas cooler, which is not shown in the diagram, and flows back again to the fans provided on the rotor 15.
The flow of the cooling gas 11 in the gas gap 14 is a flow having a certain level of circumferential-direction velocity in the direction of rotation of the rotor because of the flow of the cooling gas that is discharged from the rotor 15 and has a circumferential-direction velocity and of the friction/stirring effect of a surface of the rotor. Meanwhile, stator core inner side end portions 4t of the first inner spacers 4T are so disposed as to extend to tips of the core tooth portions 9 as much as possible, thereby keeping the stacked electromagnetic steel plates 2 bonded together.
Meanwhile, stator core inner side faces 80 of the wedges 8 are set back from inner circumference surfaces 9a of the tooth portions 9 toward the outer side. In stator core inner side openings of the ventilation ducts 5, the inner side end portions 4t of the first inner spacers 4T project toward the inner side of the stator core 1 relative to the inner circumference surfaces 80 of the wedges 8.
With the above configuration, the problems with the exhaust sections 13, in which the cooling gas 11 flows from the inner side of the stator core to the outer side, are for example as follows, as disclosed and pointed out in Japanese Patent Application Laid-Open Publication No. H08-19197 (Patent Document 1).
FIG. 17 is a schematic diagram illustrating the situation where the cooling gas 11 flows in the gas gap 14 around the exhaust section 13 and in the ventilation duct 5. As shown in FIG. 17, the cooling gas 11 that flows in a circumferential direction in the gas gap 14 needs to abruptly change direction at an inlet portion of the ventilation duct 5 so as to travel in the radial direction.
In this case, according to the configuration shown in FIG. 17, the stator core inner side end surface 80 of the wedge 8 is positioned more outer side than the stator core inner side end portion 4t of the first inner spacer 4T. Thus, the cooling gas 11 is more likely to flow into a duct 5b that is positioned on a rotor's rotation direction leading side of the stator coil 7, and it is impossible to obtain a sufficient volume of flow in a duct 5a that is positioned on a delaying side. Therefore, the problem is that it is impossible to obtain sufficient cooling performance.
Moreover, a wedge shoulder portion 16 projects into the ventilation ducts 5a and 5b. Therefore, ventilation areas become smaller and the flow becomes faster abruptly, leading to a rise in friction resistance and causing the ventilation areas to expand and contract abruptly. Therefore, there is a huge ventilation loss.
Another problem is that at a ventilation duct inlet portion of the exhaust section 13, as shown in FIG. 17, stagnant regions 17 appear at a downstream of the wedge shoulder portion 16, causing ventilation resistance to increase.
FIG. 18 is a schematic diagram illustrating the situation where the cooling gas 11 flows in the gas gap 14 around the inlet section 12 and in the ventilation duct 5.
In the inlet section 12, a huge loss (outlet loss) occurs when the cooling gas 11 is discharged into the gas gap 14 after flowing through the ventilation duct 5. According to a conventional structure in which the wedge shoulder portion 16 projects into the ventilation duct 5, ventilation areas become smaller abruptly and the flow of the cooling gas 11 being discharged into the gas gap 14 becomes faster. The increase in outlet loss is proportional to the square of the velocity of the flow. Thus, the problem is that an enormous ventilation loss occurs.
As the ventilation loss of the cooling gas 11 increases, greater power for driving fans is required to drive the cooling gas, resulting in a drop in the efficiency of the rotating electric machine. If it is impossible to obtain sufficient power for driving fans, a flow rate of the cooling gas 11 decreases, and the stator coils 7, the stator core 1, rotor coils and the like cannot be cooled sufficiently, resulting in a decrease in the reliability of the rotating electric machine's operation.
The temperatures of the stator coils 7 of the rotating electric machine are severely restricted by standards. A process of cooling the stator coils 7 plays an important role in realizing a device. In particular, because of increasing demand for power generation in recent years, the current flowing through the stator coils 7 has increased as the per-unit capacity of a power generator has grown. As a result, the amount of heat discharged from the stator coils 7 increases. Therefore, a key technical challenge is to enhance the cooling of the stator coils 7 and reduce the ventilation resistance in order to improve the performance of the rotating electric machine.
By the way, what is disclosed in Japanese Patent Application Laid-Open Publication No. H11-332142 (Patent Document 2) is a technique for adjusting the flow distribution of cooling gas that flows into ventilation ducts of a rotating electric machine in order to uniformize the temperatures of stator windings. Here, the technique disclosed in Patent Document 2 will be described with reference to FIGS. 19 and 20. FIG. 19 is a longitudinal cross-sectional view of an upper half portion of a rotating electric machine disclosed in Patent Document 2 that is positioned around a stator core. FIGS. 20(a), 20(b), 20(d) and 20(e) are diagrams showing the transverse cross-sectional shapes of wedges in portions A, B, D and E of FIG. 19, respectively, in the case of the rotating electric machine of a both-side driving type.
That is, according to the technique disclosed in Patent Document 2, cooling gas flows through a gas gap 14 between a stator core 1 and a rotor 15 in one direction, i.e. in the direction of a rotational axis (from left to right in FIG. 19), and is split flowing into a large number of ventilation ducts 5, which are arranged in an axial direction. A wedge 8 is placed near the inlet of each ventilation duct 5. The wedges 8 extend in the direction of the rotational axis so as to pass through about four to five of core blocks 3 arranged side by side in the direction of the rotational axis. In the entire rotating electric machine, five wedges 8a, 8b, 8c, 8d and 8e are arranged so as to extend in the direction of the rotational axis.
At the positions of the wedges 8 corresponding to the ventilation ducts 5, notch portions 18 are provided. The size and shape of the wedge's notch portions 18 vary appropriately according to the position of the rotational-axis direction. Since the size and shape of each notch portion 18 vary, adjustments are made to the flow distribution of cooling gas flowing into the ventilation ducts 5. That is, the wedge 8a, which is positioned at the axial-direction most upstream side of the flow of the gas gap 14, has the largest notch portions 18 as shown in FIG. 20(a). The notch portions 18 become smaller toward the axial-direction downstream side in the order that the wedges 8b, 8c and 8d are arranged. The wedge 8e, which is positioned at the most downstream side, has no notch portion.
Accordingly, the width of the wedge 8 at a position corresponding to the ventilation duct 5 is substantially equal to the width w of a slot in the case of the wedge 8a. However, the width of the other wedges 8b, 8d and 8e is larger than the width w of the slot, and the wedges 8b, 8d and 8e project into the ventilation ducts 5.
As described above, according to the technique disclosed in Patent Document 2, the size of the notch portion changes depending on the axial-direction position of the wedge. The technique does not necessarily reduce the pressure loss of the flow of the cooling gas.
The present invention has been made in view of the above circumstances. An object of the present invention is to reduce the pressure loss that occurs in the ventilation ducts in the stator core and cool down the stator coils and the stator core in an efficient manner.